1. Field of the Invention
In particular, the present invention relates to a high-pressure piston pump for supplying fuel in a common-rail circuit of an internal-combustion engine.
2. Description of the Prior Art
A piston pump of this type generally includes a pump body. A shaft, which extends along a longitudinal axis, is supported rotatably about the longitudinal axis by the pump body and has an eccentric portion and a prismatic jacking end. A first pumping station has a gear engaged with the prismatic jacking end. A second pumping station has at least one piston, which is slidable inside the pump body transversely with respect to the longitudinal axis and which is actuated by the eccentric portion of the shaft.
The first pumping station essentially has a gear pump which produces a first relatively small pressure difference, while the second pumping station generally comprises three pistons which produce a large pressure difference, also greater than 1600 bar in the high-pressure pumps which are currently manufactured, and destined to increase in order to improve further the performance features of internal-combustion engines.
The first pumping station essentially comprises a gear pump which produces a first relatively small pressure difference, while the second pumping station generally comprises three pistons which produce a large pressure difference, also greater than 1600 bar in the high-pressure pumps which are currently manufactured, and destined to increase in order to improve further the performance features of internal-combustion engines.
High-pressure pumps pose problems of wear of certain components such as the prismatic jacking end of the shaft which, during use, is engaged with a gear generally made of sintered material. At present, the actuating shaft of a high-pressure pump is made of 16MnCrS5 steel which undergoes a surface hardening heat treatment. However, the prismatic jacking end is subject to greater wear than the remainder of the shaft and is the main cause of a relative short working life of the high-pressure pump.